ok this is mitsu forum but maybe someone knows why my 04 STI vibration when i shift the gear down.whats the problem?propeller shaft bushing or something?or maybe flywheel or clutch.flywheel is stock ,clutch is exedy racing

 

It could be that your clutch wasn't installed correctly. I would start with that since you have changed it. It's a good possibility that it's the culprit.

 

The exedy is grabby clutch, it could be that you're just dropping it and not letting it out smoothly. Also you'll need to rev match.